An absorptiometer to measure a transmitted light quantity is used for an automatic analysis apparatus for clinical examination. There are two kinds of measurement principles, namely a measurement principle using the following enzyme and a measurement principle using antigen-antibody reaction, in the reaction principle of a sample and a reagent in an examination item and two kinds of major reactions, namely color reaction between a substrate and an enzyme and agglutination reaction between an antigen and an antibody, are used for the reaction of a reaction liquid.
The former is biochemical analysis and LDH (lactate dehydrogenase), ALP (alkaline phosphatase), and AST (aspartate oxoglutarate aminotransferase) are named as the examination items.
The latter is immune assay and CRP (C-reactive protein), IgG (immunoglobulin), and RF (rheumatoid factor) are named as the examination items.
The concentration of a substance in blood measured at the immune assay is low and thus a high sensitivity is required. A high sensitivity has heretofore been tried in a latex immunoagglutination method for quantitating the quantity of an ingredient contained in a sample by: using a reagent produced by sensitizing (binding) an antibody on the surface of a latex particle; projecting light to a reaction liquid when the ingredient contained in the sample is recognized and agglutinated; and measuring the quantity of the light that is not scattered by a latex aggregate and has been transmitted.
As a sample analysis apparatus to analyze the quantity of an ingredient contained in a sample, an automatic analysis apparatus to irradiate a sample or a reaction liquid produced by mixing a sample and a reagent with light from a light source, measure the quantity of the transmitted light of a single wavelength or plural wavelengths obtained resultantly and compute an absorbance, and determine an ingredient quantity from the relationship between the absorbance and a concentration in accordance with the Lambert-Beer law is widely used. In such an apparatus, a plurality of cells retaining a reaction liquid are arranged circumferentially on a cell disk repeating rotation and stop and the chronological change of an absorbance is measured at regular time intervals for about 10 minutes with a prearranged transmitted light measuring unit during the rotation of the cell disk.
In an automatic analysis apparatus for clinical examination, a method of measuring the absorbance of a reaction liquid in a reaction container while it is rotated is the mainstream. The method is called a turntable discrete method. In the method, measurement is carried out once while a reaction disk on which a reaction container is set makes one revolution. The absorbance of the reaction container is measured at regular cyclic intervals.
In the turntable discrete method, reagent dispensing is carried out multiple times (R1, R2, . . . ) in one cycle. As one cycle, there are several methods including a control method of rotating a reaction disk at one revolution and a degree corresponding to the reaction container and a control method of rotating a reaction disk at a fraction of one revolution plus a degree corresponding to the number of the reaction containers. The difference between the methods depends on the layout of a reagent dispensing mechanism and the alignment of R1, R2 stirring mechanisms.
A feature of the method is to measure a reaction liquid in a reaction container at regular intervals. Another feature thereof is to be able to monitor the reaction process between a sample and a reagent during measurement.
In an automatic analysis apparatus for clinical examination, to increase sensitivity not by measuring a transmitted light quantity with a photometer but by measuring a scattered light quantity is also attempted. When a reagent making use of antigen-antibody reaction is used, an antigen contained in a sample is reacted with an antibody contained in the reagent. A reactant is produced by antigen-antibody reaction, the particle is irradiated with light, and the magnitude of the scattered light or transmitted light is measured. A light-scattering photometer, a so-called nephelometer, is used.
For example, a system of separating transmitted light from scattered light with a diaphragm and measuring an absorbance and the scattered light simultaneously (Patent Document 1), a configuration of increasing accuracy on the higher concentration side by measuring the light reflected and scattered at a large aggregate formed as a result of the advancement of agglutination reaction (Patent Document 2), and a method of measuring the respective average light quantities of forward-scattered light and backscattered light with an integrating sphere in front of and at the back of a reaction container and correcting the turbidity change caused by the misregistration of a cell (Patent Document 3) are disclosed.